JP 2000-114917A and JP 2002-359542A disclose filters that enable a reduction in the size and cost of balance filters by substituting the capacitors included in the lumped constant balun with acoustic wave resonators. JP 2000-114917A and JP 2002-359542A disclose balance filter.
In order to reduce the power consumption of mobile phone terminals, there is strong demand for the balance filter included in mobile phone terminals to have a low insertion loss characteristic. In order to achieve low-loss in the balance filter illustrated in FIG. 7, it is necessary to reduce the loss of the ladder filter itself or reduce the loss of the lumped constant balun. In order to reduce the loss of the lumped constant balun, it is necessary to improve the Q value (quality factor) of the inductors and capacitors included in the lumped constant balun. However, neither JP 2000-114917A nor JP 2002-359542A discloses a desirable design for the IDT capacitors in order to improve their Q value. It has therefore been difficult to realize a low-loss balance filter using IDT capacitors that have a high Q value.